The subject invention is directed toward the art of pipe joints and couplings and, more particularly, to an improved tube coupling. The coupling is especially suited for use in ultra-high vacuum applications and will be described with particular reference thereto; however, as will become apparent, the invention is capable of broader application and could be used in any environment under a variety of pressure conditions.
In U.S. Pat. No. 3,521,910 to Callahan, et al., there is disclosed a tube coupling which has achieved substantial commercial success and is used in both pressure and vacuum applications. It is, however, particularly suitable for ultra-high vacuum applications.
The coupling of the noted patent generally comprises first and second annular coupling components having axial through passages and end faces which extend perpendicular to the axis of the passages. An annular rib, generally of hemispherical cross-section, extends outwardly from each end face about the through passage. A smooth, flat, annular metal sealing gasket is trapped between the opposed end faces and a threaded coupling nut or nuts act to drive the coupling components toward each other to produce sealing engagement of the annular ribs with opposite sides of the annular sealing gasket.
In making up the coupling, it is highly preferable to minimize relative rotation between the coupling components and the sealing washer. The reason for this is that the relative rotary motion can produce undesirable scoring or the like on the sealing washer and/or the sealing end faces of the coupling components. This can reduce the effectiveness of the joint and leaks may sometimes result. Additionally, when torque is transmitted from the coupling nuts to the coupling components, there is a corresponding transmission to system components and tubing which is connected to the coupling components. This can produce misalignment, twisting, and sometimes even results in damage to the related system components.
In an effort to prevent the relative rotation and reduce torque transmission from the coupling nut to other system components, it has been proposed to install anti-friction thrust bearings between the coupling nut and the associated coupling component. Both standard and special ball and needle type bearing assemblies have been proposed. Although this approach generally works satisfactorily it is somewhat undesirable in that it increases the cost and complexity of the coupling assemblies. Moreover, the addition of the anti-friction thrust bearing can significantly increase the overall length of the coupling assembly. Accordingly, there exists an ongoing need for a design to prevent relative rotary movement between the sealing faces of the coupling components and/or between the coupling components and the seal ring during coupling makeup.